Ukrainian government supporters clashed with pro-Russian demonstrators in the Black Sea port of Odessa, Ukraine, on May 2, 2014. / Sergei Poliakov, AP

by Michael Winter, USA TODAY

by Michael Winter, USA TODAY

Police in the Black Sea port of Odessa said late Friday that 31 people died when a union hall was set ablaze as pro-Russia demonstrators battled in the streets with Ukrainian loyalists.

Most victims were killed by smoke, while eight others died when they jumped from the upper floors, Reuters reported. Police initially put the death toll at 38.

Late Friday, the Interfax-Ukraine news service said that in addition to those killed in the fire, 12 others lost their lives and 123 were hurt in the day's violence.

The Trade Unions House was set on fire after being occupied by pro-Moscow demonstrators, the Kyiv Post reported.

Witnesses and journalists reported that as the building burned with people inside, a crowd shouted, "Glory to Ukraine!" and "Death to enemies!"

TV footage showed people on window sills trying to escape the smoke and flames. Video later showed blackened bodies claimed to be of victims who were trapped inside.

Citing Ukrainian newspapers, the Associated Press reported that the Russian sympathizers took refuge in the trade union hall on Kulikovo Field Square after government supporters rousted their encampment outside and then burned their tents. Police said the building was set on fire with Molotov cocktails.

Earlier, police said at least four men were shot dead after a march by thousands of pro-Kiev supporters was attacked by Russian sympathizers. Molotov cocktails, explosives and paving stones were thrown during the clashes.

The day's death toll is the highest since more than 70 people died Feb. 20 on Independence Square in Kiev during the so-called EuroMaidan Revolution, which toppled pro-Russian President Viktor Yanukovich.

The fire came hours after Ukraine's new president said that "many" pro-Russian rebels had been killed or wounded in a crackdown by Ukrainian troops in eastern city of Slovyansk, which had been held for days by separatists.